wasmtime_internal_cranelift/func_environ/stack_switching/
fatpointer.rs

1use cranelift_codegen::ir;
2use cranelift_codegen::ir::InstBuilder;
3
4/// Returns the Cranelift type used to represent all of the following:
5/// - wasm values of type `(ref null $ct)` and `(ref $ct)`
6/// - equivalently: runtime values of type `Option<VMContObj>` and `VMContObj`
7/// Note that a `VMContObj` is a fat pointer consisting of a pointer to
8/// `VMContRef` and a pointer-sized revision counter. We represent this as 2 words
9/// (pointer and usize).
10pub fn fatpointer_type(env: &crate::func_environ::FuncEnvironment) -> ir::Type {
11    let ptr_bits = env.pointer_type().bits();
12    ir::Type::int((2 * ptr_bits).try_into().unwrap()).unwrap()
13}
14
15/// Turns a (possibly null) reference to a continuation object into a tuple
16/// (revision, contref_ptr). If `contobj` denotes a wasm null reference, the
17/// contref_ptr part will be a null pointer.
18pub(crate) fn deconstruct<'a>(
19    env: &mut crate::func_environ::FuncEnvironment<'a>,
20    pos: &mut cranelift_codegen::cursor::FuncCursor,
21    contobj: ir::Value,
22) -> (ir::Value, ir::Value) {
23    debug_assert_eq!(pos.func.dfg.value_type(contobj), fatpointer_type(env));
24    let ptr_ty = env.pointer_type();
25    let ptr_bits = ptr_ty.bits();
26
27    let contref = pos.ins().ireduce(ptr_ty, contobj);
28    let shifted = pos.ins().ushr_imm(contobj, i64::from(ptr_bits));
29    let revision_counter = pos.ins().ireduce(ptr_ty, shifted);
30
31    (revision_counter, contref)
32}
33
34/// Constructs a continuation object from a given contref and revision pointer.
35/// The contref_addr may be 0, to indicate that we want to build a wasm null reference.
36pub(crate) fn construct<'a>(
37    env: &mut crate::func_environ::FuncEnvironment<'a>,
38    pos: &mut cranelift_codegen::cursor::FuncCursor,
39    revision_counter: ir::Value,
40    contref_addr: ir::Value,
41) -> ir::Value {
42    let ptr_ty = env.pointer_type();
43    let ptr_bits = ptr_ty.bits();
44    let fat_ptr_ty = fatpointer_type(env);
45
46    debug_assert_eq!(pos.func.dfg.value_type(contref_addr), ptr_ty);
47    debug_assert_eq!(pos.func.dfg.value_type(revision_counter), ptr_ty);
48
49    let contref_addr = pos.ins().uextend(fat_ptr_ty, contref_addr);
50    let revision_counter = pos.ins().uextend(fat_ptr_ty, revision_counter);
51    let shifted_counter = pos.ins().ishl_imm(revision_counter, i64::from(ptr_bits));
52    let contobj = pos.ins().bor(shifted_counter, contref_addr);
53
54    contobj
55}
wasmtime_internal_cranelift/func_environ/stack_switching/fatpointer.rs

wasmtime_internal_cranelift/func_environ/stack_switching/
fatpointer.rs
